The present invention relates to a VAV (Variable Air Volume) air conditioning system having an additional by-pass air fan and mainly equipped with a micro-computer control unit, a main air supply fan motor, a by-pass fan motor, a heat exchange pipe assembly. The micro-computer control unit has a control circuit which is responsible for control of a main air supply fan motor (the supplied air flowing via the heat exchange pipe assembly to remove heat therefrom or add heat thereto ) and a by, pass air supply fan motor which delivers air without going through the heat exchange pipe assembly to a closed space, permitting both fan motors to operate stagelessly from 0 to 100% of its full capacity, so as to regulate the air conditioning capacity of the air conditioning system according to instant conditions of a closed space, keeping the temperature thereof constantly in a state of equilibrium.
As shown in FIGS. 1, 2, a conventional CAV (Constant Air Volume) air conditioning system is comprised of a motor 1, a heat exchange pipe assembly 2 and a control circuit 3. Shown in FIG. 2 is the control circuit. The control circuit 3 can only effect 3-stage speed variation, and such 3-speed motor only runs at specific fixed speeds. There are several disadvantages associated with such a conventional motor and given as follows:
1. It is difficult to control precisely the temperature of a closed room; a conventional air fan motor can only be operated in a number of fixed speeds so that a conventional air conditioning system runs adjustably in 3 options, i.e., strong (100%), medium (85% ) and weak (70%), unable to cope properly with air conditioning loadings; such performance makes a room temperature easily fluctuated, making people uncomfortable therein. PA1 2. The poor adjustability of the conventional air conditioning system makes the efficiency of the related equipment low, causing waste of electrical energy. PA1 3. The air fan motor must be operated in a number of speeds, usually in 3 speeds, to cooperate with a 3-option temperature control switch, the cost of a motor and the related control circuit is unavoidably increased.